Internal reflection infrared waveguides have been widely used to probe interfacial phenomena of semiconductor, insulator, and organic films. For example, conventional internal reflection infrared waveguides that include an attenuated total reflection (ATR) crystal have been used to probe the surfaces of semiconductor and insulator materials. As shown in FIG. 1, a film 30 is disposed on a smooth top surface of a trapezoidal ATR crystal 20. Generally, an infrared beam 10 enters one side of trapezoidal ATR crystal 20 and makes a number of total internal reflections from the top and bottom surface. Beam 10 then exits from the other side of trapezoidal ATR crystal 20. To exit the trapezoidal ATR crystal 20, the incident angle of beam 10 on the top and bottom surfaces should exceed the critical angle (θc), which is defined by:θc=sin−1(n3/n1)
where n1 is the refractive index of the optically denser ATR crystal. Further, n3 is the refractive index of a less dense medium surrounding film 30, such as, for example, air.
Upon total reflection at the smooth top surface of trapezoidal ATR crystal 20, an evanescent electric field E(z) is created that permeates into film 30 and interacts with infrared active species on and in film 30. Each reflection from the top surface of trapezoidal ATR crystal 20 adds to the infrared absorbance. This results in sub-monolayer detection sensitivity of surface adsorbates. The enhanced infrared absorbance can be converted to fractional coverage of a monolayer when properly calibrated. For a typical infrared range from 5000 to 450 cm−1, the depth of penetration for the evanescent electric field ranges from 0.2 to 1.5 μm, depending on the infrared wavenumber.
Internal reflection infrared waveguides can potentially be useful for a variety of commercial applications, such as, for example, incorporation into semiconductor manufacturing, micro-electromechanical systems (MEMS) manufacturing, and integrated biosensor manufacturing. Another promising commercial application is as diagnostic tools for real time probing of interfacial phenomena during processing of nanostructures and nanodevices. Realization of these applications, however, requires increased surface sensitivity without significant loss of infrared throughput.
Thus, there is a need to overcome these and other problems of the prior art to provide internal reflection infrared waveguides with enhanced surface sensitivity and methods for their use.